A vehicle mounts a passenger protection system for protecting a passenger in a compartment of the vehicle from a collision of the vehicle. The passenger protection system is, for example, an air bag system for protecting the passenger by inflating an air bag in case of the collision. Recently, it is requested for the passenger protection system to protect the passenger from the collision on a side of the vehicle in addition to the collision along a front-rear direction of the vehicle.
A conventional passenger protection system mounted on the vehicle is disclosed in, for example, JP-A-2007-30766 corresponding to US 2007/0024037-A1. The system includes a sensor for detecting the collision, and a determination device for determining the collision based on a detection signal from the sensor. The determination device determines based on the detection signal from the sensor whether the collision occurs. When the determination device determines that the collision occurs, the system functions a protection device such as an air bag and/or a pre-tensioner.
In the conventional passenger protection system, multiple sensors are attached to the vehicle at multiple points, respectively. Thus, the conventional passenger protection system includes multiple sensors. Further, in the conventional passenger protection system, multiple sensors function as a sensor for detecting a collision and a safing sensor for providing redundancy of the sensor for detecting the collision.
In the conventional passenger protection system, multiple sensors are arranged on doors, which are close to boarding positions of passengers, respectively. In this case, when the position of the passenger in a compartment of the vehicle is changed, a distance between the sensor for detecting the collision and the passenger is lengthened. Thus, an accuracy of protection of the passenger may be reduced. Specifically, a boarding seat (i.e., a passenger seat), on which the passenger other than a driver sits down, can be displaced (i.e., slide) largely in a front-rear direction of the vehicle (i.e., a back-and-forth direction). In this case, if the sensor is arranged at a position corresponding to a position of the boarding seat, which is displaced to one of an utmost front position and an utmost rear position, the distance between the sensor and the passenger is increased when the seat is displaced to the other of the utmost front position and the utmost rear position. Thus, the protection of the passenger may not be sufficiently provided.